1. Field of the Invention
The present invention relates to an exposure apparatus and it making method, and device manufacturing method. More particularly, the present invention relates to an exposure apparatus used to manufacture a semiconductor device and a liquid crystal display device and the like in a lithographic process and its making method, and a device manufacturing method using the exposure apparatus.
2. Description of the Related Art
Conventionally, in the photolithographic process to manufacture a semiconductor device and the like, exposure apparatus such as the so-called stepper or the so-called scanning stepper have been used. As the illuminating light for exposure apparatus such as the stepper, the emission line (g line or i line) in the ultraviolet light region emitted from an ultra-high pressure mercury lamp has been used. In recent years, however, with the requirement for higher integration in the semiconductor device pressing, in order to print a pattern with the highest integration possible on the wafer, the exposure resolution had to be improved. Therefore, inert gas or a halogen laser light source that emits an excimer laser beam having a shorter wavelength such as the KrF excimer laser beam (wavelength: 248 nm) or the ArF excimer laser beam (wavelength: 193 nm) are now becoming used as the exposure light source. It is well known, that in the case of using an excimer laser beam with a short wavelength, materials that can be used for the lens of the projection optical system at this stage are limited to materials made of fluoride crystal such as synthetic quartz, fluorite, or lithium fluoride, mainly due to the problem of transmittance of the material.
In the case of using materials such as quartz or fluorite for the lens of the projection optical system, however, it is difficult to correct the chromatic aberration in actual. Therefore, in order to prevent the image forming characteristics from deteriorating due to the chromatic aberration, what is called narrowbanding of wavelength is required, that is, to narrow the oscillation spectral width of the excimer laser beam. This narrowbanding of wavelength is performed, for example, by using the narrowbanding module (optical elements such as a combination of a prism and a grating (diffraction grating), or etalon are used) provided in the laser resonator. And, to narrowband the wavelength, the spectral width of the wavelength of the excimer laser beam supplied to the projection optical system during exposure is required to be within a predetermined wavelength at all times, and at the same time, the so-called control of wavelength stabilization is required to keep the center wavelength at a predetermined wavelength. With recent exposure apparatus using the excimer laser beam in the far ultraviolet region, the accuracy required in the narrowbanded wavelength bandwidth (spectral width) is around 1 pm (=1xc3x9710xe2x88x9212) which corresponds to around {fraction (1/300)} of the natural oscillation spectral width before being narrowbanded, and the error of the center wavelength on wavelength stabilization requires the accuracy of around xc2x10.25 pm. In addition, as a matter of course, exposure amount control is required in these exposure apparatus.
To achieve the wavelength stabilization control, the optical properties (such as the center wavelength and the spectral half-width) of the excimer laser beam need to be monitored. The wavelength monitoring portion of the excimer laser unit is made up of etalon, which is usually a Fabry-Perot spectroscope, and a line sensor to detect its fringe pattern.
In addition, to monitor and feedback control the center wavelength and the spectral half-width of the laser beam, a spectroscopic process called deconvolution is also required. This is because when an emission line spectral emitted from an isotope mercury lamp or an iron lamp serving as a reference wavelength light source is incident on the etalon structuring the wavelength monitoring portion, a fringe pattern corresponding to the center wavelength and the spectral half-width is generated. With the fringe pattern, however, a phenomenon (convolution) occurs in which the width of the spectral half-width detected is thicker than the actual spectral half-width, due to interference of the fringe pattern with the etalon interferometer. The effect of the phenomenon, therefore, must be removed.
With the pressing requirements in recent years for an improvement in throughput, the repetition frequency of the excimer laser is becoming higher, and in order to achieve the higher repetition frequency the pulse compression circuit is becoming larger, leading to a larger excimer laser unit. Thus, the recent exposure apparatus using the excimer laser unit as the exposure light source has an arrangement that houses the main body of the exposure apparatus in a chamber called an environmental chamber where conditions such as the internal pressure, temperature, and humidity are controlled with high precision at a predetermined target value. The excimer laser unit is arranged separately outside the chamber, and is connected to the main body of the exposure apparatus by a light guiding optical system, a part of which includes a beam matching unit that is an optical system for adjusting the optical axis.
However, with the exposure apparatus using the conventional excimer laser unit described above, since the excimer laser unit was arranged separately from the main body of the exposure apparatus, a phenomenon occurred in which the optical properties of the laser beam changed while the laser beam emitted from the excimer laser unit passed through the optical system such as the light guiding optical system and the illumination optical system. This change was due to the difference in environmental conditions such as the difference in temperature and pressure between the interior of the housing of the excimer laser unit and the chamber.
Accordingly, when the spectral half-width and the like was controlled based on the detection of the fringe pattern within the housing of the excimer laser unit as was described above, the center wavelength, the spectral half-width, and the degree of energy concentration of the laser beam guided to the main body of the exposure apparatus could not be maintained at a desirable value. In such a case, since the projection optical system was adjusted only to a predetermined exposure wavelength, as a consequence, chromatic aberration of the projection optical system occurred, as well as the phenomenon of the image forming characteristics such as the magnification, distortion, and focus changing.
In addition, along with the size of the excimer laser unit increasing, to cope with the increase in chip size, the size of the main body of the exposure apparatus size is also increasing due to a larger wafer diameter and a larger stage. Thus, the footprint of the exposure apparatus in the clean room is also increasing. So, to reduce the footprint, methods such as arranging the excimer laser unit in a service room that has a lower degree of cleanliness than the clean room are being employed. With this method, however, since the light guiding optical system becomes longer, the difference in environmental conditions between the chamber where the main body of the exposure apparatus is housed and the interior of the excimer laser unit becomes larger, and the change in the optical properties of the laser beam or the change in the image forming characteristics of the projection optical system becomes more apparent.
Furthermore, when the main body of the exposure apparatus and the excimer laser unit were arranged separately as with the conventional exposure apparatus, the optical axis alignment of the laser unit and the main body of the exposure apparatus had to be performed among the laser unit, the light guiding optical system, and the illumination optical system arranged inside the main body of the exposure apparatus, which made the optical axis alignment operation troublesome and time-consuming. Accordingly, the shutdown time of the exposure apparatus during maintenance operation such as exchanging the laser was long, which led to reduction in productivity creating an unfavorable situation. In addition, when the size of the stage and its speed increased as is described above, the reaction force caused by the movement of the stage also increased, thus causing the entire main body to tilt since the main body could not endure the reaction force. In such a case, the optical axis of the light guiding system and the optical axis of the illumination optical system in the main body of the exposure apparatus diverged, which consequently led to deterioration in the quality of the transferred image.
In addition, with the integration of the semiconductor device becoming higher, the pattern line width is becoming finer, and demand for a higher resolution in the exposure apparatus is pressing. Thus, a higher N.A. in the projection optical system is also required along with a shorter wavelength in the exposure wavelength. With higher N.A., the requirement of narrowbanding in the excimer laser unit is becoming tighter, and demand for a tighter spectral half-width and degree of energy concentration is pressing. When the requirement of narrowbanding becomes tighter, the fringe pattern generated by the etalon is affected by the temperature and pressure of the etalon atmosphere. Therefore, the effect of the temperature change and the atmosphere change cannot be ignored, and it becomes difficult to perform the deconvolution process.
It is also certain, that the device rule (practical minimum line width) will be finer in the future, and with the exposure apparatus of the next generation, higher alignment precision will be required. The alignment precision depends on, for example, how the distortion component is suppressed. In addition, in order to increase the depth of focus, an increase in the UDOF (usable DOF) as well as the stability in focus is required. In either case, stability in the center wavelength and controllability of the spectral half-width is required to a high degree, and this depends on how stable and precisely the deconvolution process referred to above is performed.
The present invention has been made in consideration of the situation described above, and has as its object to provide an exposure apparatus and a device manufacturing method that can improve the productivity of the microdevice with high integration, as well as reduce the production cost of the microdevice.
According to the first aspect of the present invention, there is provided an exposure apparatus which illuminates a mask where a pattern is formed with an energy beam and transfers the pattern onto a substrate, the exposure apparatus comprising: a laser unit which includes a light source portion, and emits the energy beam; a main body of the exposure apparatus which performs exposure on the substrate with the energy beam; and an environment control chamber which houses the main body of the exposure apparatus and at least a part of the light source portion.
With the exposure apparatus, since at least a part of the light source portion structuring the laser unit is housed within the same environment control chamber as the main body of the exposure apparatus, it is possible to reduce the footprint of the apparatus compared with the conventional apparatus in which the entire laser unit is arranged separately from the main body of the exposure apparatus. In addition, environmental conditions such as the temperature or pressure of a part of, or the entire light source portion and the main body of the exposure apparatus can be maintained the same, and this makes it possible to suppress the shift of the center wavelength of the laser beam, change in spectral half-width and the degree of energy concentration due to the temperature difference between the light source portion and the main body of the exposure apparatus. Accordingly, for example, by suppressing the change in the degree of energy concentration, the controllability in the exposure amount improves, leading to improvement in exposure accuracy. Therefore, with the present invention, due to reduction in the footprint of the apparatus, the equipment cost of the clean room can be reduced which leads to a decrease in the production cost of the microdevice. And the improvement in exposure accuracy leads to an improvement in yield, resulting in improving the productivity of the microdevice.
In this case, the main body of the exposure apparatus may include a projection optical system which projects the energy beam onto the substrate. In such a case, chromatic aberration of the projection optical system due to the wavelength shift, change in magnification, image forming characteristics such as focus and distortion can be suppressed, and as a consequence, the exposure accuracy (including the overlay accuracy) can be improved.
In this case, the laser unit may be a laser unit which emits a pulse ultraviolet light of a wavelength less than 300 nm. Fluoride crystal such as fluorite is mainly used as the glass material of the projection optical system when light having such wavelength is used, and in the case of using such material, it is actually difficult to correct the chromatic aberration. Therefore, it can be said that the present invention which can almost suppress the chromatic aberration of the projection optical system shows great effectiveness.
With the exposure apparatus related to the present invention, a part of the light source portion housed in the environment control chamber may include at least a laser resonator.
xe2x80x9cLaser resonator,xe2x80x9d here, refers not only to the laser emitting light source itself, but also refers to the entire unit in the case when the laser emitting light source and the wavelength narrowbanding element is integrated, and is used in this sense throughout the description.
In such a case, since a part of the light source portion which include the laser resonator structuring the laser unit is housed in the same environment control chamber as the main body of the exposure apparatus, the footprint of the apparatus can be reduced similarly as above. And the environmental conditions such as temperature and pressure can be maintained practically the same between the laser resonator and the main body of the exposure apparatus. Moreover, since the optical path of the laser beam becomes shorter than the case when the laser unit is arranged separately, the change in spectral half-width of the laser beam while passing through the optical path becomes smaller, and the number of optical components for light guiding can be reduced. Accordingly, the cost of the apparatus can be reduced, resulting in further reduction of the production cost of the microdevice.
In this case, it is preferable for the laser resonator to emit a pulse ultraviolet light of a wavelength less than 180 nm. With the exposure apparatus using pulse ultraviolet light having such a wavelength as the illumination light for exposure, the glass material used is limited to fluoride crystal such as fluorite, which is costly, therefore, the effect of the reduction of optical components described above becomes larger.
With the exposure apparatus related to the present invention, in the case the laser resonator is housed within the same environment control chamber as the main body of the exposure apparatus, the exposure apparatus can further comprise: an illumination optical system which guides the energy beam from the laser resonator to the mask; and a supporting member on which the laser resonator and at least a part of the illumination optical system is arranged. In such a case, when maintenance operation such as exchanging the laser resonator is performed, the coinciding operation of the optical axes of can be performed easily just by matching the optical axes of the laser resonator and the illumination optical system, thus reducing the downtime of the apparatus. In addition, even if the main body of the exposure apparatus tilts due to the movement of the stage, there is no deviation between the laser resonator and at least a part of the illumination optical system, therefore, the deterioration of the transferred image due to the deviation of the optical axes can be avoided. Accordingly, the productivity of the microdevice such as a semiconductor element can be further improved.
In this case, the illumination optical system may have a first partial optical system arranged on the supporting member and a second partial optical system arranged on a frame in the main body side of the exposure apparatus, and an optical integrator may be arranged in the second partial optical system near a border of the first partial optical system. In such a case, even if the main body of the exposure apparatus tilts due to the movement of the substrate stage which structures the main body of the exposure apparatus, there is no deviation between the laser resonator and the first partial illumination optical system. Moreover, since the optical integrator is arranged in the second partial optical system near the border of the first partial optical system, the deviation of the optical axis of the first partial optical system in respect to the second partial optical system is not a serious problem. Therefore, the deterioration of the transferred image due to the deviation of the optical axes can be avoided.
With the exposure apparatus related to the present invention, in the case the laser resonator and at least a part of the illumination optical system is arranged on the same supporting member, the part of the light source portion housed in the environment control chamber may further include a wavelength monitoring portion and a reference wavelength light source, and at least one of the wavelength monitoring portion and the reference wavelength light source may be arranged on the supporting member.
With the exposure apparatus related to the present invention, the part of the light source portion housed in the environment control chamber may include at least a wavelength monitoring portion and a reference wavelength light source. In such a case, since the wavelength monitoring portion structuring the laser unit and its reference wavelength light source is arranged within the same environment chamber as the main body of the exposure apparatus, the shift of the center wavelength due to temperature difference or pressure difference between the reference wavelength light source and the wavelength monitoring portion, change in spectral half-width and the degree of energy concentration can be suppressed to a minimum, and the change in the image forming characteristics of the projection optical system due to these factors, for example, such as change in focus and distortion can be suppressed to a minimum. Accordingly, the pattern can be transferred with higher precision.
In this case, when the laser unit is a KrF excimer laser unit, the reference wavelength light source may be an Ar ion second harmonic laser light source. The center wavelength of the Ar ion second harmonic laser light source (wavelength: 248.253 nm) is extremely close to the designed wavelength of the KrF excimer laser (wavelength: 248.385 nm) and is suitable for reference, and since the spectral half-width is extremely narrow (less than 0.01 pm) the deconvolution process can be performed with high precision, and the stability of the center wavelength and the controllability of the spectral half-width can be secured at a high degree. Accordingly, the change in image forming characteristics, especially the distortion component can be effectively suppressed and the overlay accuracy can be improved, as well as increase the UDOF and increase the depth of focus due to the stability of focus secured.
With the exposure apparatus related to the present invention, in the case a part of the light source portion housed in the environment control chamber includes at least a wavelength monitoring portion and a reference wavelength light source, the exposure apparatus can further comprise: an optical path switching unit which selectively chooses an energy beam incident on the wavelength monitoring portion from a laser resonator structuring the laser unit and the reference wavelength light source; and a control unit which performs calibration of the wavelength monitoring portion by guiding an energy beam from the reference wavelength light source into the wavelength monitoring portion via the optical path switching unit. In such a case, calibration of the wavelength monitoring portion can be performed by the control unit guiding in the energy beam from the reference wavelength light source via the optical path switching unit. Therefore, calibration of the wavelength monitoring portion (calibration of the energy beam from the laser resonator with the energy beam from the reference wavelength light source as a reference) can be performed at an appropriate interval, which makes it possible to maintain the center wavelength and the spectral half-width and the like of the energy beam emitted from the laser resonator at a desired value. As a consequence, the chromatic aberration of the projection optical system can be almost suppressed, and exposure with high precision can be performed.
In this case, it is preferable for the control unit to perform calibration of the wavelength monitoring portion during non-exposure when irradiation of the energy beam on the substrate is not required. In such a case, the calibration of the wavelength monitoring portion hardly has any effect on the throughput of the exposure apparatus. For example, the control unit may perform calibration of the wavelength monitoring portion in parallel with an exchanging process of one of the mask and the substrate, or the control unit may perform calibration of the wavelength monitoring portion in parallel with an alignment process.
With the exposure apparatus related to the present invention, in the case a part of the light source portion housed in the environment control chamber includes at least a wavelength monitoring portion and a reference wavelength light source, the part of the light source portion housed in the environment control chamber may further include a laser resonator. In such a case, as is described earlier, it is possible to reduce the footprint of the apparatus, as well as practically maintain the environmental conditions such as the temperature and pressure the same between the laser resonator and the main body of the exposure apparatus. In addition, on maintenance operations such as exchanging the laser resonator, the coinciding operation of the optical axes can be performed easily, thus reducing the downtime of the apparatus.
With the exposure apparatus related to the present invention, in the case a part of the light source portion housed in the environment control chamber includes a wavelength monitoring portion, a reference wavelength light source, and a laser resonator, the exposure apparatus can further comprise a control unit which performs temperature adjustment of said light source portion and said main body of said exposure apparatus so that temperature of all optical systems within said environment control chamber is uniform as a whole. In such a case, the shift in center wavelength of the laser beam, the change in spectral half-width and the degree of energy concentration due to the temperature difference between the light source portion and the main body of the exposure apparatus can be prevented. Accordingly, change in the magnification of the projection optical system, image forming characteristics such as focus and distortion, can be suppressed to a minimum.
According to the second aspect of the present invention, there is provided a making method of an exposure apparatus which exposes a substrate by an energy beam, the making method including: providing a laser unit which includes a light source portion, and emits the energy beam; providing an illumination system which illuminates a mask on which a pattern is formed with the energy beam from the laser unit; providing a main body of the exposure apparatus which transfers the pattern onto the substrate, the main body including a projection optical system which projects the energy beam outgoing from the mask onto the substrate; and providing an environment chamber which houses the main body of the exposure apparatus and at least a part of the light source portion.
With this making method, the exposure apparatus of the present invention can be made by incorporating the illumination optical system, the projection optical system, and other various components into the main body of the exposure apparatus, combining and adjusting these parts mechanically, electrically, and optically, and furthermore, housing at least a part of the light source portion of the laser unit and the main body of the exposure apparatus in the environment control chamber. In this case, for example, a static type projection exposure apparatus based on the step-and-repeat method can be made.
With the making method of the exposure apparatus related to the present invention, the making method may further include providing a driving unit which synchronously moves the mask and the substrate in a linear direction. In such a case, for example, a scanning type exposure apparatus based on a step-and-scan method can be made.
In addition, by using the exposure apparatus in the present invention to perform exposure in a lithographic process, a multiple layer of patterns can be accurately overlaid and formed on a substrate, which allows a microdevice with high integration to be produced with high yield, improving the productivity. Accordingly, from another aspect of the present invention, there is provided a device manufacturing method that uses the exposure apparatus of the present invention.